diff --git a/mercurial/exchange.py b/mercurial/exchange.py
--- a/mercurial/exchange.py
+++ b/mercurial/exchange.py
@@ -806,9 +806,26 @@ def _pushb2phases(pushop, bundler):
     if 'phases' in pushop.stepsdone:
         return
     b2caps = bundle2.bundle2caps(pushop.remote)
-    if 'pushkey' in b2caps:
+    ui = pushop.repo.ui
+
+    legacyphase = 'phases' in ui.configlist('devel', 'legacy.exchange')
+    haspushkey = 'pushkey' in b2caps
+    hasphaseheads = 'heads' in b2caps.get('phases', ())
+
+    if hasphaseheads and not legacyphase:
+        _pushb2phaseheads(pushop, bundler)
+    elif haspushkey:
         _pushb2phasespushkey(pushop, bundler)
 
+def _pushb2phaseheads(pushop, bundler):
+    """push phase information through a bundle2 - binary part"""
+    pushop.stepsdone.add('phases')
+    if pushop.outdatedphases:
+        updates = [[] for p in phases.allphases]
+        updates[0].extend(h.node() for h in pushop.outdatedphases)
+        phasedata = phases.binaryencode(updates)
+        bundler.newpart('phase-heads', data=phasedata)
+
 def _pushb2phasespushkey(pushop, bundler):
     """push phase information through a bundle2 - pushkey part"""
     pushop.stepsdone.add('phases')
diff --git a/tests/test-acl.t b/tests/test-acl.t
--- a/tests/test-acl.t
+++ b/tests/test-acl.t
@@ -97,7 +97,7 @@ Extension disabled for lack of a hook
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -117,17 +117,15 @@ Extension disabled for lack of a hook
   adding quux/file.py revisions
   added 3 changesets with 3 changes to 3 files
   bundle2-input-part: total payload size 1553
-  bundle2-input-part: "pushkey" (params: 4 mandatory) supported
-  pushing key for "phases:911600dab2ae7a9baff75958b84fe606851ce955"
+  bundle2-input-part: "phase-heads" supported
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   updating the branch cache
-  bundle2-output-bundle: "HG20", 2 parts total
+  bundle2-output-bundle: "HG20", 1 parts total
   bundle2-output-part: "reply:changegroup" (advisory) (params: 0 advisory) empty payload
-  bundle2-output-part: "reply:pushkey" (params: 0 advisory) empty payload
   bundle2-input-bundle: no-transaction
   bundle2-input-part: "reply:changegroup" (advisory) (params: 0 advisory) supported
-  bundle2-input-part: "reply:pushkey" (params: 0 advisory) supported
-  bundle2-input-bundle: 1 parts total
+  bundle2-input-bundle: 0 parts total
   listing keys for "phases"
   repository tip rolled back to revision 0 (undo push)
   0:6675d58eff77
@@ -162,7 +160,7 @@ Extension disabled for lack of acl.sourc
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -184,17 +182,15 @@ Extension disabled for lack of acl.sourc
   calling hook pretxnchangegroup.acl: hgext.acl.hook
   acl: changes have source "push" - skipping
   bundle2-input-part: total payload size 1553
-  bundle2-input-part: "pushkey" (params: 4 mandatory) supported
-  pushing key for "phases:911600dab2ae7a9baff75958b84fe606851ce955"
+  bundle2-input-part: "phase-heads" supported
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   updating the branch cache
-  bundle2-output-bundle: "HG20", 2 parts total
+  bundle2-output-bundle: "HG20", 1 parts total
   bundle2-output-part: "reply:changegroup" (advisory) (params: 0 advisory) empty payload
-  bundle2-output-part: "reply:pushkey" (params: 0 advisory) empty payload
   bundle2-input-bundle: no-transaction
   bundle2-input-part: "reply:changegroup" (advisory) (params: 0 advisory) supported
-  bundle2-input-part: "reply:pushkey" (params: 0 advisory) supported
-  bundle2-input-bundle: 1 parts total
+  bundle2-input-bundle: 0 parts total
   listing keys for "phases"
   repository tip rolled back to revision 0 (undo push)
   0:6675d58eff77
@@ -230,7 +226,7 @@ No [acl.allow]/[acl.deny]
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -262,17 +258,15 @@ No [acl.allow]/[acl.deny]
   acl: branch access granted: "911600dab2ae" on branch "default"
   acl: path access granted: "911600dab2ae"
   bundle2-input-part: total payload size 1553
-  bundle2-input-part: "pushkey" (params: 4 mandatory) supported
-  pushing key for "phases:911600dab2ae7a9baff75958b84fe606851ce955"
+  bundle2-input-part: "phase-heads" supported
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   updating the branch cache
-  bundle2-output-bundle: "HG20", 2 parts total
+  bundle2-output-bundle: "HG20", 1 parts total
   bundle2-output-part: "reply:changegroup" (advisory) (params: 0 advisory) empty payload
-  bundle2-output-part: "reply:pushkey" (params: 0 advisory) empty payload
   bundle2-input-bundle: no-transaction
   bundle2-input-part: "reply:changegroup" (advisory) (params: 0 advisory) supported
-  bundle2-input-part: "reply:pushkey" (params: 0 advisory) supported
-  bundle2-input-bundle: 1 parts total
+  bundle2-input-bundle: 0 parts total
   listing keys for "phases"
   repository tip rolled back to revision 0 (undo push)
   0:6675d58eff77
@@ -308,7 +302,7 @@ Empty [acl.allow]
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -336,6 +330,7 @@ Empty [acl.allow]
   acl: branch access granted: "ef1ea85a6374" on branch "default"
   error: pretxnchangegroup.acl hook failed: acl: user "fred" not allowed on "foo/file.txt" (changeset "ef1ea85a6374")
   bundle2-input-part: total payload size 1553
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
@@ -375,7 +370,7 @@ fred is allowed inside foo/
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -407,6 +402,7 @@ fred is allowed inside foo/
   acl: branch access granted: "911600dab2ae" on branch "default"
   error: pretxnchangegroup.acl hook failed: acl: user "fred" not allowed on "quux/file.py" (changeset "911600dab2ae")
   bundle2-input-part: total payload size 1553
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
@@ -447,7 +443,7 @@ Empty [acl.deny]
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -475,6 +471,7 @@ Empty [acl.deny]
   acl: branch access granted: "ef1ea85a6374" on branch "default"
   error: pretxnchangegroup.acl hook failed: acl: user "barney" not allowed on "foo/file.txt" (changeset "ef1ea85a6374")
   bundle2-input-part: total payload size 1553
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
@@ -516,7 +513,7 @@ fred is allowed inside foo/, but not foo
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -548,6 +545,7 @@ fred is allowed inside foo/, but not foo
   acl: branch access granted: "911600dab2ae" on branch "default"
   error: pretxnchangegroup.acl hook failed: acl: user "fred" not allowed on "quux/file.py" (changeset "911600dab2ae")
   bundle2-input-part: total payload size 1553
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
@@ -590,7 +588,7 @@ fred is allowed inside foo/, but not foo
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -620,6 +618,7 @@ fred is allowed inside foo/, but not foo
   acl: branch access granted: "f9cafe1212c8" on branch "default"
   error: pretxnchangegroup.acl hook failed: acl: user "fred" denied on "foo/Bar/file.txt" (changeset "f9cafe1212c8")
   bundle2-input-part: total payload size 1553
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
@@ -661,7 +660,7 @@ fred is allowed inside foo/, but not foo
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -689,6 +688,7 @@ fred is allowed inside foo/, but not foo
   acl: branch access granted: "ef1ea85a6374" on branch "default"
   error: pretxnchangegroup.acl hook failed: acl: user "barney" not allowed on "foo/file.txt" (changeset "ef1ea85a6374")
   bundle2-input-part: total payload size 1553
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
@@ -734,7 +734,7 @@ barney is allowed everywhere
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -766,17 +766,15 @@ barney is allowed everywhere
   acl: branch access granted: "911600dab2ae" on branch "default"
   acl: path access granted: "911600dab2ae"
   bundle2-input-part: total payload size 1553
-  bundle2-input-part: "pushkey" (params: 4 mandatory) supported
-  pushing key for "phases:911600dab2ae7a9baff75958b84fe606851ce955"
+  bundle2-input-part: "phase-heads" supported
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   updating the branch cache
-  bundle2-output-bundle: "HG20", 2 parts total
+  bundle2-output-bundle: "HG20", 1 parts total
   bundle2-output-part: "reply:changegroup" (advisory) (params: 0 advisory) empty payload
-  bundle2-output-part: "reply:pushkey" (params: 0 advisory) empty payload
   bundle2-input-bundle: no-transaction
   bundle2-input-part: "reply:changegroup" (advisory) (params: 0 advisory) supported
-  bundle2-input-part: "reply:pushkey" (params: 0 advisory) supported
-  bundle2-input-bundle: 1 parts total
+  bundle2-input-bundle: 0 parts total
   listing keys for "phases"
   repository tip rolled back to revision 0 (undo push)
   0:6675d58eff77
@@ -819,7 +817,7 @@ wilma can change files with a .txt exten
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -851,6 +849,7 @@ wilma can change files with a .txt exten
   acl: branch access granted: "911600dab2ae" on branch "default"
   error: pretxnchangegroup.acl hook failed: acl: user "wilma" not allowed on "quux/file.py" (changeset "911600dab2ae")
   bundle2-input-part: total payload size 1553
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
@@ -899,7 +898,7 @@ file specified by acl.config does not ex
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -922,6 +921,7 @@ file specified by acl.config does not ex
   acl: checking access for user "barney"
   error: pretxnchangegroup.acl hook raised an exception: [Errno *] * (glob)
   bundle2-input-part: total payload size 1553
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
@@ -974,7 +974,7 @@ betty is allowed inside foo/ by a acl.co
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -1006,6 +1006,7 @@ betty is allowed inside foo/ by a acl.co
   acl: branch access granted: "911600dab2ae" on branch "default"
   error: pretxnchangegroup.acl hook failed: acl: user "betty" not allowed on "quux/file.py" (changeset "911600dab2ae")
   bundle2-input-part: total payload size 1553
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
@@ -1060,7 +1061,7 @@ acl.config can set only [acl.allow]/[acl
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -1092,17 +1093,15 @@ acl.config can set only [acl.allow]/[acl
   acl: branch access granted: "911600dab2ae" on branch "default"
   acl: path access granted: "911600dab2ae"
   bundle2-input-part: total payload size 1553
-  bundle2-input-part: "pushkey" (params: 4 mandatory) supported
-  pushing key for "phases:911600dab2ae7a9baff75958b84fe606851ce955"
+  bundle2-input-part: "phase-heads" supported
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   updating the branch cache
-  bundle2-output-bundle: "HG20", 2 parts total
+  bundle2-output-bundle: "HG20", 1 parts total
   bundle2-output-part: "reply:changegroup" (advisory) (params: 0 advisory) empty payload
-  bundle2-output-part: "reply:pushkey" (params: 0 advisory) empty payload
   bundle2-input-bundle: no-transaction
   bundle2-input-part: "reply:changegroup" (advisory) (params: 0 advisory) supported
-  bundle2-input-part: "reply:pushkey" (params: 0 advisory) supported
-  bundle2-input-bundle: 1 parts total
+  bundle2-input-bundle: 0 parts total
   listing keys for "phases"
   repository tip rolled back to revision 0 (undo push)
   0:6675d58eff77
@@ -1148,7 +1147,7 @@ fred is always allowed
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -1180,17 +1179,15 @@ fred is always allowed
   acl: branch access granted: "911600dab2ae" on branch "default"
   acl: path access granted: "911600dab2ae"
   bundle2-input-part: total payload size 1553
-  bundle2-input-part: "pushkey" (params: 4 mandatory) supported
-  pushing key for "phases:911600dab2ae7a9baff75958b84fe606851ce955"
+  bundle2-input-part: "phase-heads" supported
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   updating the branch cache
-  bundle2-output-bundle: "HG20", 2 parts total
+  bundle2-output-bundle: "HG20", 1 parts total
   bundle2-output-part: "reply:changegroup" (advisory) (params: 0 advisory) empty payload
-  bundle2-output-part: "reply:pushkey" (params: 0 advisory) empty payload
   bundle2-input-bundle: no-transaction
   bundle2-input-part: "reply:changegroup" (advisory) (params: 0 advisory) supported
-  bundle2-input-part: "reply:pushkey" (params: 0 advisory) supported
-  bundle2-input-bundle: 1 parts total
+  bundle2-input-bundle: 0 parts total
   listing keys for "phases"
   repository tip rolled back to revision 0 (undo push)
   0:6675d58eff77
@@ -1232,7 +1229,7 @@ no one is allowed inside foo/Bar/
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -1262,6 +1259,7 @@ no one is allowed inside foo/Bar/
   acl: branch access granted: "f9cafe1212c8" on branch "default"
   error: pretxnchangegroup.acl hook failed: acl: user "fred" denied on "foo/Bar/file.txt" (changeset "f9cafe1212c8")
   bundle2-input-part: total payload size 1553
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
@@ -1310,7 +1308,7 @@ OS-level groups
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -1343,17 +1341,15 @@ OS-level groups
   acl: branch access granted: "911600dab2ae" on branch "default"
   acl: path access granted: "911600dab2ae"
   bundle2-input-part: total payload size 1553
-  bundle2-input-part: "pushkey" (params: 4 mandatory) supported
-  pushing key for "phases:911600dab2ae7a9baff75958b84fe606851ce955"
+  bundle2-input-part: "phase-heads" supported
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   updating the branch cache
-  bundle2-output-bundle: "HG20", 2 parts total
+  bundle2-output-bundle: "HG20", 1 parts total
   bundle2-output-part: "reply:changegroup" (advisory) (params: 0 advisory) empty payload
-  bundle2-output-part: "reply:pushkey" (params: 0 advisory) empty payload
   bundle2-input-bundle: no-transaction
   bundle2-input-part: "reply:changegroup" (advisory) (params: 0 advisory) supported
-  bundle2-input-part: "reply:pushkey" (params: 0 advisory) supported
-  bundle2-input-bundle: 1 parts total
+  bundle2-input-bundle: 0 parts total
   listing keys for "phases"
   repository tip rolled back to revision 0 (undo push)
   0:6675d58eff77
@@ -1395,7 +1391,7 @@ OS-level groups
   bundle2-output-part: "check:phases" 24 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 24 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -1427,6 +1423,7 @@ OS-level groups
   acl: branch access granted: "f9cafe1212c8" on branch "default"
   error: pretxnchangegroup.acl hook failed: acl: user "fred" denied on "foo/Bar/file.txt" (changeset "f9cafe1212c8")
   bundle2-input-part: total payload size 1553
+  bundle2-input-part: total payload size 24
   bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
@@ -1509,13 +1506,12 @@ No branch acls specified
   f9cafe1212c8c6fa1120d14a556e18cc44ff8bdd
   911600dab2ae7a9baff75958b84fe606851ce955
   e8fc755d4d8217ee5b0c2bb41558c40d43b92c01
-  bundle2-output-bundle: "HG20", 6 parts total
+  bundle2-output-bundle: "HG20", 5 parts total
   bundle2-output-part: "replycaps" 168 bytes payload
   bundle2-output-part: "check:phases" 48 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 48 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -1551,21 +1547,15 @@ No branch acls specified
   acl: branch access granted: "e8fc755d4d82" on branch "foobar"
   acl: path access granted: "e8fc755d4d82"
   bundle2-input-part: total payload size 2068
-  bundle2-input-part: "pushkey" (params: 4 mandatory) supported
-  pushing key for "phases:911600dab2ae7a9baff75958b84fe606851ce955"
-  bundle2-input-part: "pushkey" (params: 4 mandatory) supported
-  pushing key for "phases:e8fc755d4d8217ee5b0c2bb41558c40d43b92c01"
-  bundle2-input-bundle: 5 parts total
+  bundle2-input-part: "phase-heads" supported
+  bundle2-input-part: total payload size 48
+  bundle2-input-bundle: 4 parts total
   updating the branch cache
-  bundle2-output-bundle: "HG20", 3 parts total
+  bundle2-output-bundle: "HG20", 1 parts total
   bundle2-output-part: "reply:changegroup" (advisory) (params: 0 advisory) empty payload
-  bundle2-output-part: "reply:pushkey" (params: 0 advisory) empty payload
-  bundle2-output-part: "reply:pushkey" (params: 0 advisory) empty payload
   bundle2-input-bundle: no-transaction
   bundle2-input-part: "reply:changegroup" (advisory) (params: 0 advisory) supported
-  bundle2-input-part: "reply:pushkey" (params: 0 advisory) supported
-  bundle2-input-part: "reply:pushkey" (params: 0 advisory) supported
-  bundle2-input-bundle: 2 parts total
+  bundle2-input-bundle: 0 parts total
   listing keys for "phases"
   repository tip rolled back to revision 2 (undo push)
   2:fb35475503ef
@@ -1600,13 +1590,12 @@ Branch acl deny test
   f9cafe1212c8c6fa1120d14a556e18cc44ff8bdd
   911600dab2ae7a9baff75958b84fe606851ce955
   e8fc755d4d8217ee5b0c2bb41558c40d43b92c01
-  bundle2-output-bundle: "HG20", 6 parts total
+  bundle2-output-bundle: "HG20", 5 parts total
   bundle2-output-part: "replycaps" 168 bytes payload
   bundle2-output-part: "check:phases" 48 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 48 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -1641,7 +1630,8 @@ Branch acl deny test
   acl: path access granted: "911600dab2ae"
   error: pretxnchangegroup.acl hook failed: acl: user "astro" denied on branch "foobar" (changeset "e8fc755d4d82")
   bundle2-input-part: total payload size 2068
-  bundle2-input-bundle: 5 parts total
+  bundle2-input-part: total payload size 48
+  bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
   abort: acl: user "astro" denied on branch "foobar" (changeset "e8fc755d4d82")
@@ -1677,13 +1667,12 @@ Branch acl empty allow test
   f9cafe1212c8c6fa1120d14a556e18cc44ff8bdd
   911600dab2ae7a9baff75958b84fe606851ce955
   e8fc755d4d8217ee5b0c2bb41558c40d43b92c01
-  bundle2-output-bundle: "HG20", 6 parts total
+  bundle2-output-bundle: "HG20", 5 parts total
   bundle2-output-part: "replycaps" 168 bytes payload
   bundle2-output-part: "check:phases" 48 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 48 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -1712,7 +1701,8 @@ Branch acl empty allow test
   acl: acl.deny not enabled
   error: pretxnchangegroup.acl hook failed: acl: user "astro" not allowed on branch "default" (changeset "ef1ea85a6374")
   bundle2-input-part: total payload size 2068
-  bundle2-input-bundle: 5 parts total
+  bundle2-input-part: total payload size 48
+  bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
   abort: acl: user "astro" not allowed on branch "default" (changeset "ef1ea85a6374")
@@ -1750,13 +1740,12 @@ Branch acl allow other
   f9cafe1212c8c6fa1120d14a556e18cc44ff8bdd
   911600dab2ae7a9baff75958b84fe606851ce955
   e8fc755d4d8217ee5b0c2bb41558c40d43b92c01
-  bundle2-output-bundle: "HG20", 6 parts total
+  bundle2-output-bundle: "HG20", 5 parts total
   bundle2-output-part: "replycaps" 168 bytes payload
   bundle2-output-part: "check:phases" 48 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 48 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -1785,7 +1774,8 @@ Branch acl allow other
   acl: acl.deny not enabled
   error: pretxnchangegroup.acl hook failed: acl: user "astro" not allowed on branch "default" (changeset "ef1ea85a6374")
   bundle2-input-part: total payload size 2068
-  bundle2-input-bundle: 5 parts total
+  bundle2-input-part: total payload size 48
+  bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
   abort: acl: user "astro" not allowed on branch "default" (changeset "ef1ea85a6374")
@@ -1817,13 +1807,12 @@ Branch acl allow other
   f9cafe1212c8c6fa1120d14a556e18cc44ff8bdd
   911600dab2ae7a9baff75958b84fe606851ce955
   e8fc755d4d8217ee5b0c2bb41558c40d43b92c01
-  bundle2-output-bundle: "HG20", 6 parts total
+  bundle2-output-bundle: "HG20", 5 parts total
   bundle2-output-part: "replycaps" 168 bytes payload
   bundle2-output-part: "check:phases" 48 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 48 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -1859,21 +1848,15 @@ Branch acl allow other
   acl: branch access granted: "e8fc755d4d82" on branch "foobar"
   acl: path access granted: "e8fc755d4d82"
   bundle2-input-part: total payload size 2068
-  bundle2-input-part: "pushkey" (params: 4 mandatory) supported
-  pushing key for "phases:911600dab2ae7a9baff75958b84fe606851ce955"
-  bundle2-input-part: "pushkey" (params: 4 mandatory) supported
-  pushing key for "phases:e8fc755d4d8217ee5b0c2bb41558c40d43b92c01"
-  bundle2-input-bundle: 5 parts total
+  bundle2-input-part: "phase-heads" supported
+  bundle2-input-part: total payload size 48
+  bundle2-input-bundle: 4 parts total
   updating the branch cache
-  bundle2-output-bundle: "HG20", 3 parts total
+  bundle2-output-bundle: "HG20", 1 parts total
   bundle2-output-part: "reply:changegroup" (advisory) (params: 0 advisory) empty payload
-  bundle2-output-part: "reply:pushkey" (params: 0 advisory) empty payload
-  bundle2-output-part: "reply:pushkey" (params: 0 advisory) empty payload
   bundle2-input-bundle: no-transaction
   bundle2-input-part: "reply:changegroup" (advisory) (params: 0 advisory) supported
-  bundle2-input-part: "reply:pushkey" (params: 0 advisory) supported
-  bundle2-input-part: "reply:pushkey" (params: 0 advisory) supported
-  bundle2-input-bundle: 2 parts total
+  bundle2-input-bundle: 0 parts total
   listing keys for "phases"
   repository tip rolled back to revision 2 (undo push)
   2:fb35475503ef
@@ -1913,13 +1896,12 @@ push foobar into the remote
   f9cafe1212c8c6fa1120d14a556e18cc44ff8bdd
   911600dab2ae7a9baff75958b84fe606851ce955
   e8fc755d4d8217ee5b0c2bb41558c40d43b92c01
-  bundle2-output-bundle: "HG20", 6 parts total
+  bundle2-output-bundle: "HG20", 5 parts total
   bundle2-output-part: "replycaps" 168 bytes payload
   bundle2-output-part: "check:phases" 48 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 48 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -1955,21 +1937,15 @@ push foobar into the remote
   acl: branch access granted: "e8fc755d4d82" on branch "foobar"
   acl: path access granted: "e8fc755d4d82"
   bundle2-input-part: total payload size 2068
-  bundle2-input-part: "pushkey" (params: 4 mandatory) supported
-  pushing key for "phases:911600dab2ae7a9baff75958b84fe606851ce955"
-  bundle2-input-part: "pushkey" (params: 4 mandatory) supported
-  pushing key for "phases:e8fc755d4d8217ee5b0c2bb41558c40d43b92c01"
-  bundle2-input-bundle: 5 parts total
+  bundle2-input-part: "phase-heads" supported
+  bundle2-input-part: total payload size 48
+  bundle2-input-bundle: 4 parts total
   updating the branch cache
-  bundle2-output-bundle: "HG20", 3 parts total
+  bundle2-output-bundle: "HG20", 1 parts total
   bundle2-output-part: "reply:changegroup" (advisory) (params: 0 advisory) empty payload
-  bundle2-output-part: "reply:pushkey" (params: 0 advisory) empty payload
-  bundle2-output-part: "reply:pushkey" (params: 0 advisory) empty payload
   bundle2-input-bundle: no-transaction
   bundle2-input-part: "reply:changegroup" (advisory) (params: 0 advisory) supported
-  bundle2-input-part: "reply:pushkey" (params: 0 advisory) supported
-  bundle2-input-part: "reply:pushkey" (params: 0 advisory) supported
-  bundle2-input-bundle: 2 parts total
+  bundle2-input-bundle: 0 parts total
   listing keys for "phases"
   repository tip rolled back to revision 2 (undo push)
   2:fb35475503ef
@@ -2008,13 +1984,12 @@ Branch acl conflicting deny
   f9cafe1212c8c6fa1120d14a556e18cc44ff8bdd
   911600dab2ae7a9baff75958b84fe606851ce955
   e8fc755d4d8217ee5b0c2bb41558c40d43b92c01
-  bundle2-output-bundle: "HG20", 6 parts total
+  bundle2-output-bundle: "HG20", 5 parts total
   bundle2-output-part: "replycaps" 168 bytes payload
   bundle2-output-part: "check:phases" 48 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 48 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -2043,7 +2018,8 @@ Branch acl conflicting deny
   acl: acl.deny not enabled
   error: pretxnchangegroup.acl hook failed: acl: user "george" denied on branch "default" (changeset "ef1ea85a6374")
   bundle2-input-part: total payload size 2068
-  bundle2-input-bundle: 5 parts total
+  bundle2-input-part: total payload size 48
+  bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
   abort: acl: user "george" denied on branch "default" (changeset "ef1ea85a6374")
@@ -2080,13 +2056,12 @@ User 'astro' must not be denied
   f9cafe1212c8c6fa1120d14a556e18cc44ff8bdd
   911600dab2ae7a9baff75958b84fe606851ce955
   e8fc755d4d8217ee5b0c2bb41558c40d43b92c01
-  bundle2-output-bundle: "HG20", 6 parts total
+  bundle2-output-bundle: "HG20", 5 parts total
   bundle2-output-part: "replycaps" 168 bytes payload
   bundle2-output-part: "check:phases" 48 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 48 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -2122,21 +2097,15 @@ User 'astro' must not be denied
   acl: branch access granted: "e8fc755d4d82" on branch "foobar"
   acl: path access granted: "e8fc755d4d82"
   bundle2-input-part: total payload size 2068
-  bundle2-input-part: "pushkey" (params: 4 mandatory) supported
-  pushing key for "phases:911600dab2ae7a9baff75958b84fe606851ce955"
-  bundle2-input-part: "pushkey" (params: 4 mandatory) supported
-  pushing key for "phases:e8fc755d4d8217ee5b0c2bb41558c40d43b92c01"
-  bundle2-input-bundle: 5 parts total
+  bundle2-input-part: "phase-heads" supported
+  bundle2-input-part: total payload size 48
+  bundle2-input-bundle: 4 parts total
   updating the branch cache
-  bundle2-output-bundle: "HG20", 3 parts total
+  bundle2-output-bundle: "HG20", 1 parts total
   bundle2-output-part: "reply:changegroup" (advisory) (params: 0 advisory) empty payload
-  bundle2-output-part: "reply:pushkey" (params: 0 advisory) empty payload
-  bundle2-output-part: "reply:pushkey" (params: 0 advisory) empty payload
   bundle2-input-bundle: no-transaction
   bundle2-input-part: "reply:changegroup" (advisory) (params: 0 advisory) supported
-  bundle2-input-part: "reply:pushkey" (params: 0 advisory) supported
-  bundle2-input-part: "reply:pushkey" (params: 0 advisory) supported
-  bundle2-input-bundle: 2 parts total
+  bundle2-input-bundle: 0 parts total
   listing keys for "phases"
   repository tip rolled back to revision 2 (undo push)
   2:fb35475503ef
@@ -2169,13 +2138,12 @@ Non-astro users must be denied
   f9cafe1212c8c6fa1120d14a556e18cc44ff8bdd
   911600dab2ae7a9baff75958b84fe606851ce955
   e8fc755d4d8217ee5b0c2bb41558c40d43b92c01
-  bundle2-output-bundle: "HG20", 6 parts total
+  bundle2-output-bundle: "HG20", 5 parts total
   bundle2-output-part: "replycaps" 168 bytes payload
   bundle2-output-part: "check:phases" 48 bytes payload
   bundle2-output-part: "check:heads" streamed payload
   bundle2-output-part: "changegroup" (params: 1 mandatory) streamed payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
-  bundle2-output-part: "pushkey" (params: 4 mandatory) empty payload
+  bundle2-output-part: "phase-heads" 48 bytes payload
   bundle2-input-bundle: with-transaction
   bundle2-input-part: "replycaps" supported
   bundle2-input-part: total payload size 168
@@ -2204,7 +2172,8 @@ Non-astro users must be denied
   acl: acl.deny not enabled
   error: pretxnchangegroup.acl hook failed: acl: user "george" denied on branch "default" (changeset "ef1ea85a6374")
   bundle2-input-part: total payload size 2068
-  bundle2-input-bundle: 5 parts total
+  bundle2-input-part: total payload size 48
+  bundle2-input-bundle: 4 parts total
   transaction abort!
   rollback completed
   abort: acl: user "george" denied on branch "default" (changeset "ef1ea85a6374")
diff --git a/tests/test-bundle2-exchange.t b/tests/test-bundle2-exchange.t
--- a/tests/test-bundle2-exchange.t
+++ b/tests/test-bundle2-exchange.t
@@ -252,9 +252,6 @@ push
   remote: added 1 changesets with 0 changes to 0 files (-1 heads)
   remote: 1 new obsolescence markers
   remote: pre-close-tip:eea13746799a public book_eea1
-  remote: pushkey: lock state after "phases"
-  remote: lock:  free
-  remote: wlock: free
   remote: pushkey: lock state after "bookmarks"
   remote: lock:  free
   remote: wlock: free
@@ -392,9 +389,6 @@ push over http
   remote: added 1 changesets with 1 changes to 1 files
   remote: 1 new obsolescence markers
   remote: pre-close-tip:32af7686d403 public book_32af
-  remote: pushkey: lock state after "phases"
-  remote: lock:  free
-  remote: wlock: free
   remote: pushkey: lock state after "bookmarks"
   remote: lock:  free
   remote: wlock: free
diff --git a/tests/test-push-http.t b/tests/test-push-http.t
--- a/tests/test-push-http.t
+++ b/tests/test-push-http.t
@@ -70,7 +70,6 @@ expect success
   remote: adding manifests
   remote: adding file changes
   remote: added 1 changesets with 1 changes to 1 files
-  remote: pushkey hook: HG_HOOKNAME=pushkey HG_HOOKTYPE=pushkey HG_KEY=ba677d0156c1196c1a699fa53f390dcfc3ce3872 HG_NAMESPACE=phases HG_NEW=0 HG_OLD=1 HG_RET=1
   remote: phase-move: cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b:  1 -> 0
   remote: phase-move: ba677d0156c1196c1a699fa53f390dcfc3ce3872:   -> 0
   remote: changegroup hook: HG_BUNDLE2=1 HG_HOOKNAME=changegroup HG_HOOKTYPE=changegroup HG_NODE=ba677d0156c1196c1a699fa53f390dcfc3ce3872 HG_NODE_LAST=ba677d0156c1196c1a699fa53f390dcfc3ce3872 HG_SOURCE=serve HG_TXNID=TXN:$ID$ HG_URL=remote:http:$LOCALIP: (glob)
@@ -89,7 +88,6 @@ expect success, server lacks the httphea
   remote: adding manifests
   remote: adding file changes
   remote: added 1 changesets with 1 changes to 1 files
-  remote: pushkey hook: HG_HOOKNAME=pushkey HG_HOOKTYPE=pushkey HG_KEY=ba677d0156c1196c1a699fa53f390dcfc3ce3872 HG_NAMESPACE=phases HG_NEW=0 HG_OLD=1 HG_RET=1
   remote: phase-move: cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b:  1 -> 0
   remote: phase-move: ba677d0156c1196c1a699fa53f390dcfc3ce3872:   -> 0
   remote: changegroup hook: HG_BUNDLE2=1 HG_HOOKNAME=changegroup HG_HOOKTYPE=changegroup HG_NODE=ba677d0156c1196c1a699fa53f390dcfc3ce3872 HG_NODE_LAST=ba677d0156c1196c1a699fa53f390dcfc3ce3872 HG_SOURCE=serve HG_TXNID=TXN:$ID$ HG_URL=remote:http:$LOCALIP: (glob)
@@ -108,7 +106,6 @@ expect success, server lacks the unbundl
   remote: adding manifests
   remote: adding file changes
   remote: added 1 changesets with 1 changes to 1 files
-  remote: pushkey hook: HG_HOOKNAME=pushkey HG_HOOKTYPE=pushkey HG_KEY=ba677d0156c1196c1a699fa53f390dcfc3ce3872 HG_NAMESPACE=phases HG_NEW=0 HG_OLD=1 HG_RET=1
   remote: phase-move: cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b:  1 -> 0
   remote: phase-move: ba677d0156c1196c1a699fa53f390dcfc3ce3872:   -> 0
   remote: changegroup hook: HG_BUNDLE2=1 HG_HOOKNAME=changegroup HG_HOOKTYPE=changegroup HG_NODE=ba677d0156c1196c1a699fa53f390dcfc3ce3872 HG_NODE_LAST=ba677d0156c1196c1a699fa53f390dcfc3ce3872 HG_SOURCE=serve HG_TXNID=TXN:$ID$ HG_URL=remote:http:$LOCALIP: (glob)
@@ -124,6 +121,8 @@ expect push success, phase change failur
   > allow_push = *
   > [hooks]
   > prepushkey = sh -c "printenv.py prepushkey 1"
+  > [devel]
+  > legacy.exchange=phases
   > EOF
   $ req
   pushing to http://localhost:$HGPORT/
@@ -144,6 +143,8 @@ expect phase change success
 
   $ cat >> .hg/hgrc <<EOF
   > prepushkey = sh -c "printenv.py prepushkey 0"
+  > [devel]
+  > legacy.exchange=
   > EOF
   $ req
   pushing to http://localhost:$HGPORT/
@@ -152,7 +153,6 @@ expect phase change success
   remote: adding manifests
   remote: adding file changes
   remote: added 1 changesets with 1 changes to 1 files
-  remote: prepushkey hook: HG_BUNDLE2=1 HG_HOOKNAME=prepushkey HG_HOOKTYPE=prepushkey HG_KEY=ba677d0156c1196c1a699fa53f390dcfc3ce3872 HG_NAMESPACE=phases HG_NEW=0 HG_NODE=ba677d0156c1196c1a699fa53f390dcfc3ce3872 HG_NODE_LAST=ba677d0156c1196c1a699fa53f390dcfc3ce3872 HG_OLD=1 HG_PENDING=$TESTTMP/test HG_PHASES_MOVED=1 HG_SOURCE=serve HG_TXNID=TXN:$ID$ HG_URL=remote:http:$LOCALIP: (glob)
   % serve errors
   $ hg rollback
   repository tip rolled back to revision 0 (undo serve)